Paper mill boil out methods and compositions



Jan. 1, 1963 E. w. DUNKLIN ETAL 3,071,504

PAPER MILL BOIL OUT METHODS .AND COMPOSITIONS Filed May 12. 1958 PROV/0fAouEoL/s soLur/cw CONTAIN/N6 a/-5.0% 6) 14/5/6717 0F AlAAL/Nf CLEA NlA/GAGENT AND 0. col-1.0% 0F SEQUESTf'R/NG AeEm; E s00- IUM GLUCOHEPTONATEwmv THl-S SOLUTION FILL PORTIONS OF PAPER M/LL. SYSTEM TO BE CLEANEDCIRCULATE THESOLUT/ON THROUGH SUCH POR T/ONS AT ELEVATED TEMPERATUREBELOW 2/2 F.

REMOVE THE SOLUTION FROM THE SYSTEM LEAV- //\/6- SURFACE AREAS OF THESYSTEM FREE FROM DEPOSITS OF POLYVALEN METAL H)- DROX/DES BUT WITH AMATERIAL DEPOSIT OF THE SEQUESTERING AGENT PLACE PAPER M/LL m/ OPERATIONE02 P20000- 770/v OF PAPER THE 0EPos/r 0F SEQUESTE/Z/NG AGENT PREvE/vfwaDEPOSIT OF OBJECT/UNABLE AMOUNTS 0F POLYVALENT METAL COMPOUNDS o/v sucHSUPFACE AeEAs ream THE CIRCULAT- ING WATER 'OF THE PAPER MILL lNVE/V T028 EDWARD 1M DL/A/KL/N MAB/E K- MOUDEY United States Patent Ofitice3,191, 12:

3,071,504 PAPER MILL BUHL OUT METHODS AND CQMPOSITIIGNS Edward W.Dunklin, Port Arthur, Ontario, Canada, and

Marie K. Moudry, Northiield, 111., assignors to United States MovidynCorporation, Chicago, 111., a corporation of Illinois Filed May 12,195%, Star. No. 734,404 2 Claims. (Cl. 162--199) This invention relatesto the operation of paper mills and particularly to an improved methodfor preparing paper mills for operation, and to a novel paper mill boilout composition employed in such method.

During the operation of paper mills, very substantial amounts ofdeposited materials collect on the surfaces of the liquid circulatingsystem of the mill and it is necessary to shut the mill downoccasionally to remove such deposits. Th usual method of removal is theboil out, involving pumping a hot caustic solution through the liquidcirculating system of the mill, the caustic being employed to dissolvethe deposits so that the same are removed by the flowing solution.

We have observed that the troublesome deposits which form in paper millcirculating systems are mainly those of calcium and iron. We have alsodiscovered that the conventional boil out methods, while havingconsiderable effectiveness in removing some of the deposits, actuallyhave a tendency to promote further troublesome deposits when the mill isplaced into operation following the boil out procedure. Thisresults'because the hydroxides of the polyvalent amphoteric metals areprecipitated onto the walls and surfaces of the equipment and becausetraces of the alkaline components of the boil out solution remain on theequipment. Thus, whil the conventional method may leave the solidsurfaces of the circulating system apparently clean, the presence of thehydroxides of the polyvalent amphoteric metals, and the alkaline boilout components, on the apparently clean surfaces brings about a speedyand voluminous deposit of didtional compounds from the circulating waterin the mill during paper-making operation.

We have also observed that, among the hydroxides left on the apparentlyclean surfaces by the conevntional boil out methods are those of ironand that the presence of iron is exceedingly objectionable. This isbecause the deposits formed during operation of the mill will include amaterial amount of the iron left by the boil out procedure and this ironwill then feed sulfate bacteria, with the result that some of thedeposits built up in the circulating system during the paper-makingoperation are of very dark color. After a time, some of these darkdeposits begin to break away, flowing with the recirculating waters ofthe mill and thus being introduced into the paper being made, with theresult that the paper is spoiled.

We have discovered that the foregoing disadvantages can b successfullyovercome by carrying out the boil out method wtih a hot aqueous solutionof (1) an alkaline cleaning agent substantially free from addedcompounds of calcium, and (2) an eflective proportion of a sequesteringagent capable of sequestering calcium, iron and other polyvalentamphoteric metal ions but incapable of efiectively sequestering sodium,potassium or ammonium. When both the alkaline cleaning agent and such asequestering agent are employed, the polyvalent metal hydroxides whichwould normally be precipitated from the boil out solution are tied up bythe sequestering agent. Additionally, after the boil out is completed, amaterial amount of the sequestering agent is left on the solid surfacesof the various parts of the mill forming the circulatingsystem, so thatthe tendency toward pre cipitation of polyvalent metal compounds, oncethe'mill is put back into use, is eliminated or greatly reduced.

Since the sequestering agent employed must, on the one hand, be capableof effective removal of the polyvalent metal ions always present in theboil out water, while, on the other hand, not acting to decrease theeffectiveness of the alkaline cleaning agent, it is apparent that thesequestering agent must be carefully selected. We have found that, whilemany commercially available sequestering agents are unsatisfactory foruse in boil out compositions, highly satisfactory results are obtainedif the sequestering agent is selected from the group consisting of thesugar acids, the alkali metal, alkaline earth metal and ammonium saltsof the sugar acids, and sorbitol. Of this class of compounds, theglucoheptonates are unusually advantageous, sodium glucoheptonate beinga particularly efiective agent. Other typical compounds which may beused are gluconic acid, sodium glucoheptonate, saccharic acid andpotassium sodium saccaharate.

The alkaline cleaning agents useful in accordance with the inventioninclude sodium hydroxide, which is prticu- 'larly effective, potassiumhydroxide, sodium carbonate, the various phosphates and polyphosphatesof sodium or potassium, ammonium hydroxide, the silicates of sodium orpotassium, sodium metasilicate being particularly useful, and the soaps,such as sodium oleate, sodium stearate and the usual saponified fattyglyceride mixtures of commerce. For paper mill situations of usualseverity, sodium hydroxide or potasisum hydroxide are frequently themost feasible alkaline cleaning agents.

Advantageously, we first prepare a boil out composition comprising atleast one of the alkaline cleaning compounds and the specialsequestering agent, the latter being included in proportions equal tol20% of the weight of the alkaline compound employed. Such compositionis then added to the boil out water to provide a solution in which theconcentration of the alkaline cleaning compound is (Ll-5.0% by weight.Thus, the concentration of the special sequestering agent is 0.ll0ll.0%by weight.

Such compositions can be either aqueous solutions or dry mixtures. Inthe case of solutions, the alkaline cleaning compound can be employed inproportions equal to 350% by weight of the total composition, with theproportion of sequestering agent equal to 03-10% by weight. In the caseof dry mixtures, and assuming no additional ingredients, such asextenders, etc., are employed, the composition comprises -99% by weightof the alkaline cleaning compound and l-20% by weight of the specialsequestering agent.

Whether liquid or dry mixture, the compositions can advantageouslyinclude a substantial proportion of an insoluble inorganic abrasivematerial capable of aiding the boil out solution in removing deposits.Bentonite and other clay-like minerals are especially effective. Whenthe boil out composition is prepared as an aqueous solution, thebentonite or like abrasive material can be employed in amounts up to 5%by weight of the composition. When a dry mixture is employed, thebentonite or the like can be employed in amounts up to about 10% of thecombined weight of alkaline cleaning compound and sequestering agent.

The alkaline cleaning compound and special sequestering agent, or thecomposition containing the same, can be added to the boil out watereither before or after the water is introduced into the circulatingsystem to be cleaned, and the Water is then heated to the temperaturedesirable for circulation through the system. Alternatively, the watercan be introduced into the system and then heated, the alkaline cleaningcompound and special sequestering agent being introduced into the hotwater. The solution is passed through the circulating system at anelevated temperature below the boiling point, advantageously at leastabout 180 F. While normal boil out methods call for circulation times onthe order of several hours, these times can be considerably reduced whenemploying the present invention, though it will be understood that theduration of treatment will of course vary, depending upon the severityof the situation encountered in the mill. It will also be understoodthat the volume of solution employed is dependent upon each particularcase. All that is required is that a sufficient amount of solution beemployed to fill those portions of the system through which the solutionis to be circulated.

Thus, the method of the present invention is carried out in accordancewith the flowsheet constituting the single figure of the accompanyingdrawings.

The following examples are illustrative:

Example I A paper mill which has been shut down because of theoccurrence of extensive deposits on the walls of the liquid circulatingsystem is treated as follows: 5,000 gallons of water is introduced intoa stock storage chest and heated to 180 F. by the introduction of livesteam. During heating of the water, sodium hydroxide and a mixture ofa-sodium glucoheptonate and b-sodium gluco heptonate are added at ratesproviding a solution containing 1% by weight of the caustic and .05% byweight of the sequestering agent. When the solution has been adequatelyheated, it is continuously circulated, by the pumps of the circulatingsystem, through the circulating system for a period of four hours.During such circulation, the deposits on the walls of the circulatingsystem are gradually removed. The boil out solution is then pumped outof the system and the paper mill put promptly into operation.

Where, employing ordinary boil out procedures, with out the specialcomposition of this example, it would normally be necessary to run themill for as much as 8-l0 hours on start-up before obtaining salablepaper, the mill treated in accordance with this example can be put intosuccessful operation much more promptly, the startup time being limited,under normal circumstances, to that required for obtaining properoperation without giving consideration to the effect of boil outresidues.

Example 2 The procedure of Eaxrnple l is repeated, adding the sodiumhydroxide at a rate providing a concentration thereof of approximately4% and adding the sequestering agent at a rate providing a concentrationthereof of 1%. The time for circulation of the boil out solution soprepared is shortened to two hours in view of the increasedconcentration of the caustic and sequestering agent.

In both of the foregoing examples, it will be found that theobjectionable deposits are much more readily and completely removed thanin the case of conventional boil out methods. The danger that somedeposits will be only partially treated, and will thus break looseduring the start-up of the mill, is accordingly substantiallyeliminated. It will also be found that there is much less tendencytoward formation of deposits early in the operation of the paper mill,after the boil out treatment, and that there is less tendency towardoccurrence of sulfate bacteria.

As a general rule, depending upon the severity of the conditionsencountered in the mill, better cleaning of the circulating system, andlonger successful operation of the mill in the making of paper followingcleaning, are obtained when the proportion of the special sequesteringagent is increased.

Example 3 The procedure of Example 2 is repeated, using potassiumhydroxide as the caustic material and employing the same proportions ofcaustic and sequestering agent. Again, successful cleaning isaccomplished in a relatively shorter time than is usually employed, andthe surfaces of the system are left substantially free of precipitatedbydroxides.

Example 4 The procedure of Example 1 is repeated, using sorbitol as thesequestering agent and increasing the amount there'- of to provide asorbitol concentration of 1% by weight. The results are equivalent tothose obtained in Example 1.

Example 5 A liquid boil out composition is prepared by dissolving 30parts by weight sodium hydroxide and 3 parts by weight of mixed a-sodiumglucoheptonate and b-sodium giucoheptonate in 67 parts by weight water.This composition is used to clean a paper mill by feeding the liquidcomposition into a stock storage chest filled with water, heating thewater to between 180 F. and 200 F., and circulating the resultingsolution through the recirculating system of the mill. The compositionis added to the stock chest in an amount equal to 10% of the watertherein, so that the concentration of the caustic in the boil out wateris 3% and that of the glucoheptonate 0.3%, by weight. This proceduregives a thorough removal of deposits in a relatively shorter time thanhas been usual for conventional boil out compositions, leaving thesystem substantially free of precipitated hydroxides.

Example 6 A dry boil out composition is prepared by blending parts byweight sodium hydroxide and 20 parts by weight of mixed a-sodiurnglucoheptonate and b-sodium glucoheptonate. The composition istransported as dry mix to the point of use and then introduced into theboil out water after the same has been placed in the system and heated.Both compounds being highly soluble, agitation, other than bycirculation of the water, is ordinarily not required. The drycomposition is added in such amount as to provide a concentration of thesodium hydroxide on the order of 23%, and of the glucoheptonate,(LS-0.75%, by weight, for normally severe deposits in the mill.

Example 7 Example 5 is repeated, employing in addition to theglucoheptonate and sodium hydroxide an amount of bentonite equal to 5%by weight of the liquid composition. The composition is employed in thesame manner as in Example 5. Including bentonite as an abradant, thecomposition acts more quickly in those cases where the deposits in thecirculating system of the mill are encrusted and unusually tenacious.

Example 8 Example 6 is repeated, employing in the dry mixture 10 partsby weight bentonite. The dry composition is employed as in Example 6,but is more rapid in its cleaning action than the composition of thatexample when encrusted and unusually tenacious deposits are encountered.

We claim:

1. The method for preparing the liquid circulating system of a papermill for use comprising providing in the system an aqueous solutioncontaining 0.15.0% by weight of at least one alkaline cleaning agent and0.001- 1.0%, by weight of at least one sequestering agent selected fromthe group consisting of the sugar acids, the alkali metal, alkalineearth metal and ammonium salts of the sugar acids, and sorbitol, thevolume of such solution being such as to substantially fill thoseunitary por tions of the paper mill system to be cleaned, thencirculating said solution at an elevated temperature below 212 F.through those portions of the system to be cleaned, removing thesolution from the system and thereby leaving surface areas of the systemsubstantially free from deposits of polyvalent metal hydroxides but witha material deposit of such sequestering agent, and then placing the millinto operation for production of paper, the presence of said materialdeposit of such sequestering agent being efiective to prevent thedeposit on said surface areas of objectionable amounts of precipitatedpolyvalent metal compounds from the circulating water in the mill whenthe mill is placed in operation.

2. The method for preparing the liquid circulating system of a papermill for use comprising introducing into the liquid circulating system avolume of Water sufiicient for circulation through those portions of thesystem to be cleaned, incorporating into the water at least one alkalinecleaning agent and at least one sequestering agent selected from thegroup consisting of the sugar acids, the alkali metal, alkaline earthmetal and ammonium salts of the sugar acids, and sorbitol, inproportions sufficient to provide a solution containing 0.1-5 .0% byweight of said cleaning agent and 0.0011.0% by weight of thesequestering agent, heating the water to 180-200 F., circulating theresulting hot solution through those portions of the system to becleaned, removing the solution from the system and thereby leavingsurface areas of the system carrying a small but material amount of saidsequestering agent but substantially free from deposits of polyvalentmetal hydroxides, and then placing the mill into operation for theproduction of paper, the presence of said material amount of saidsequestering agent being efiective to prevent the deposit on saidsurface areas of objectionable amounts of precipitated polyvalent metalcompounds from the circulating water in the mill when the mill is placedin operation.

References Cited in the tile of this patent UNITED STATES PATENTS OTHERREFERENCES Casey: Pulp and Paper, vol. I, page 679, copyright 1952.

Sequestrene, booklet by Geigy Industrial Chemicals, copyright 1952, pp.30, 35, 36, 47, 48 and 50.

Condensed Chemical Dictionary, 5th Ed., pp. 138, 288, 739, pub. byReinhold Pub. Corp., New York (1956).

1. THE METHOD FOR PREPARING THE LIQUID CIRCULATING SYSTEM OF A PAPERMILL FOR USE COMPRISING PROVIDING IN THE SYSTEM AN AQUEOUS SOLTUIONCONTAINING 0.1-5.0% BY WEIGHT OF AT LEAST ONE SEQUESTERING AGENT SE1.0%BY WEIGHT OF AT LEAST ONE SEQUESTERING AGENT SELECTED FROM THE GROUPCONSISTING OF THE SUGAR ACIDS, THE ALKALI METAL, ALKALINE EARTH METALAND AMMONIMUM SALTS OF THE SUGAR ACIDS, AND SORBITOL, THE VOLUME OF SUCHSOLUTION BEING SUCH AS TO SUBSTANTIALLY FILL THOSE UNITARY PORTIONS OFTHE PAPER MILL SYSTEM TO BE CLEANED, THEN CIRCULATING SAID SOLUTION ATAN ELEVATED TEMPERATURE BELOW 212* F. THROUGH THOSE PORTIONS OF THESYSTEM TO BE CLEANED, REMOVING THE SOLUTION FROM THE SYSTEM AND THEREBYLEAVING SURFACE AREAS OF THE SYSTEM SUBSTANTIALLY FREE FROM DEPOSITS OFPOLYVALNT METAL HYDROXIDES BUT WITH A MATERIAL DEPOSIT OF SUCHSEQUESTERING AGENT, AND THEN PLACING THE MILL INTO OPERATION FORPRODUCTION OF PAPER, THE PRESENCE OF SAID MATERIAL DEPOSIT OF SUCHSEQUESTERING AGENT BEING EFFECTIVE TO PREVENT THE DEPOSIT ON SAIDSURFACE AREAS OF OBJECTIONABLE AMOUNTS OF PRECIPITATED POLYVALENT METALCOMPOUNDS FROM THE CIRCULATING WATER IN THE MILL WHEN THE MILL IS PLACEDIN OPERATION.